Acoustic electromagnetic transducer device having means for protecting coil-wire insulation



ACOUSTIC ELECTROMAGNETIC TRANSDUCER DEVICE HAVING MEANS FOR L. BERCOVICI Jan. 20, 1970 PROTECTING COIL-WIRE INSULATION Filed March 14, 1967 M8. I C 0" 7 5 2 4% .9 3. m I I MW m 7 4.. 5 H uwuwvwvwvwu m 3 76 lg! EE 7 I? F 4 E 3 M a 6 f 1 3 U K. 1 l E d B M J 4 S a 2 4 M 2 6 max mm 4 F. 2 m 8 4 a U 4 m u r\. M/ 7.WN/| 3 w n 3 I, L m 1. H. mh/k M B United States Patent 3,491,215 ACOUSTIC ELECTROMAGNETIC TRANSDUCER DEVICE HAVING MEANS FOR PROTECTING COIL-WIRE INSULATION Lucian Bercovici, Wilbraham, Mass., assignor to Sonotone Corporation, Elmsford, N.Y., a corporation of New York Filed Mar. 14, 1967, Ser. No. 623,087 Int. Cl. H04r 13/02 U.S. Cl. 179114 8 Claims ABSTRACT OF THE DISCLOSURE An acoustic electromagnetic transducer having a magnetic core structure with two core legs passing permanent magnetic flux operates with a long alternating-flux carrying flat vibratory magnetic reed having a transverse crossing reed arm adjoining nearby core end poles and an opposite free vibratory reed end carried in an air gap between opposite core and poles. The two spool walls are joined to each other by two narrow connector rods which are pressed into afiixing engagement with the opposite edges of the reed by the increasing tension of the coil turns wound on the previously positioned spool. The spool connector rods are somewhat thicker, as by a few mills, than the reed to protect the coil-wire insulation against damage by any sharp portions of the reed edge. A thin drive rod connected with its outer rod end to the diaphragm and joined with its inward rod end to a portion of a nearby transverse spool wall and is either integrally formed with the spool or is otherwise aifixed thereto for securing conjoined vibrations of the reed and the diaphragm.

This invention relates to acoustic signal transducers of the type described in US. Patent 2,927,976 having an electromagnetic system with a virbating reed for transducing acoustic signals into electric signals and vice-versa. More specifically, the invention relates to subminiature acoustic reed transducers which may be combined, for example, with a transistor amplifier into a complete subminiature hearing aid small enough for hidden wear in a narrow eyeglass-frame temple, or behind the ear, or within the outer ear cavity. As an example, the specific acoustic reed transducer of the invention described in detail hereafter has an overall size of only 0.470" long, 0.250 wide and 0.127" high. In all such prior reed transducers, the thin magnetic reed had to be mounted for vibration free from interference within an extremely narrow fiat interior spool space of its transducing windings, and this requirement has presented critical problems.

Among the objects of the invention is such reed type acoustic transducer which overcomes the difficulties presented by the need for freedom from interference of the vibrating reed within the minute fiat spool space of its transducing windings.

In a transducer device of the invention, the vibratory reed extends from a transverse mounting arm thereof and the spool with the coil winding surrounds and are affixed to the vibratory reed and vibrate therewith. Since the affixed windings materially increases the reed stiffness or reduces its compliance, its transverse mounting arm is affixed to the system at two opposite arm portions which are spaced from the mounting end of the reed so that an unclamped intermediate part of the tranverse reed arm will vibrate with the reed and thereby increase its compliance.

More specifically, the acoustic reed transducer of the invention is characterized among others by the following features:

With the two spaced spool heads held affixed to the reed by the narrow spool connectors having substantially the same thickness and clampingly engaging the reed edges, the process of affixing the coil with the spool to the reed is greatly simplified. The spool is first pushed into its operative position on the reed near the reed cross arm without any coil turns on the spool. Only after the spool is properly located in the operative position on the reed with the two narrow spool head connectors engaging the reed edges, the coil is wound around the narrow spool connectors thereby reducing to a minimum the thickness of the coil in a direction perpendicular to the plane of the reed and thereby materially reducing the overall thickness of the transducer in a direction perpendicular to the planes of the reed and the overlying diaphragm. The coil clamps and aflixes itself to the reed as it is being wound around the two narrow spool connectors between the two transverse spool end walls.

By affixing the inward end of the narrow diaphragmreed connector rod to the nearby transverse spool wall, there is eliminated the separate operation of aifixing the inward driving rod end to the reed. This feature makes it possible to mold the diaphragm-drive rod in the spool molding operation since the drive rod is integrally formed with adjacent transverse spool wall. The spool with the integrally formed drive rod on the reed without any coil turns on the spool makes it possible to accurately position or locate the spool in the required operative position on the reed near the reed crossarm and without any operative interference therewith. Thereupon, the coil is wound on the spool having its integrally formed diaphragm-drive rod located in the proper operative position on the reed.

The foregoing and other objects of the invention will be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawings, showing all parts greatly enlarged, wherein:

FIG. 1 is a central vertical cross-sectional view of an example of an acoustic-reed transducer of the invention;

FIG. 2 is a transverse cross-sectional view of the transducer along lines 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view along lines 3-3 of FIG. 2;

FIG. 4 is a perspective view of one form of the new reed-coil combination of the same transducer;

FIG. 5 is a plan view of the same new reed-coil combination, the coil being shown in cross-section.

FIG. 5A is a cross sectional view taken along the lines 5A5A of FIGURE 5; and

FIG. 6 is a simplified diagrammatical view of the operative relationship of the ferromagnetic system and the reed-coil arrangement of such transducer of the invention.

Referring to FIGS. 1 through 6, the acoustic transducer 10 comprises a vibratory diaphragm 11 which is connected through a drive rod 12 to a vibratory armature or reed 13 of an electromagnetic signal transducer structure. On the vibratory reed 13 is held a spool 21 with a coil of transducer windings 22 wound thereon. The vibratory reed is part of a cooperating ferromagnetic core structure generally designated 30. The armature reed 13 is of lowretentivity, high permeability ferromagnetic material, and

is of flat cross-section and extends with its flat surface in a plane perpendicular to the surface of FIG. 1.

Except for the new features of the reed-coil combinations of the invention as described herein, the ferromagnetic core structure 30 is of conventional design and it may, for example, be a duplicate of that used in similar prior-art transducers such as described in US. Patent 2,927,976 of H. A. Pearson.

The transducer of FIGS. 1 to 6 comprises a core structure having two magnetic core members 31, 41 permeable to permanent magnetic flux and extending generally parallel and opposite to each other adjacent and parallel to the opposite flat surfaces of the reed 13. The reed 13 has a freely vibrating reed end 13-1 and at its opposite end a reed support section or arm- 14 extending transversely or perpendicularly to the reed 13. The transverse reed arm 14 has two spaced mounting portions 15 and an intermediate or central reed arm section 16 from the center of which the reed 13 projects. The spool 21 with its coil 22 is held affixed to the leftward part of vibrating reed 13 adjoining the transverse reed arm 14.

In the specific form shown in FIGS. 1 to 5, the core structure has two core members 31, 41 with one leftward set of opposite inwardly projecting pole portions 32, 42 having substantially fiat pole faces spaced by small air gap 33 within which the free reed end 131 vibrates. At their leftward side, the core members 31, 41 have two core pole end regions 34, 44 overlying the opposite surfaces of transverse reed arm 16. The intermediate or central part of the leftward core pole end regions 34, 44 is spaced by a relatively large space from the facing central section 16 of transverse reed arm 14 (FIG. 3). Only the two remote mounting portions 15 of transverse reed arm 14 are held clamped in proper position between the two opposite-polarity pole projections 34 and 44 of the two core bodies 31, 41 (FIGS. 1, 3, 6). The two opposite core pole projections 34 and 44 are suitably atfixed or clamped to the two spaced reed arm mounting ends 15 as by screws across thin conventional non-magnetic spacers or shims 37.

The desired permanent magnetic polarization of the two opposite pole cores 31 and 41 is supplied by a permanent magnet 45 extending between the rightward opposite core end regions 39, 49 of the two cores (FIGS. 1, 2, 3, 4). The permanent magnetization of magnet 45 magnetizes the spaces between two pairs of opposite poles of the two cores 31, 41 as indicated by N and S marks applied to the respective pairs of opposite core poles 32, 42 and 34, 44. When the reed 13 is in neutral position and the coil 22 deenergized, the reed 13 will remain in neutral balanced position with respect to the permanently magnetized pole cores 31, 41. When the reed 13 is vibrated, as by the diaphragm, the free reed end -131 will alternatively approach the faces of opposite core poles 32 and 42 and send oppositely directed alternating magnetic flux through coil 22 for generating signals corresponding to the vibrations. Signal currents through the coil 22 causes the reed 13 to vibrate and generate with the diaphragm a corresponding acoustic output.

The intermediate reed arm portion 16 adjoining the reed 13 is free to vibrate and its compliance increases with that of the reed-coil unit 13, 21 thereby lowering the resonant frequency of the vibrating reed-coil unit 13, 21. As an example, it is desirable that the mass and the so increased higher compliance of the reed-coil unit should be proportioned to cause the reed-coil unit 13, 21 to vibrate with a resonant frequency in the lower part of the audio-frequency range, for example, below 1000 c.p.s., such as 800 to 900 c.p.s. The compliance of the intermediate reed-arm portion 16 may be increased by recesses or notches 17 in the two arm portions adjoining the two fixed remote arm mounting sections 15, so that gives it higher compliance.

As an example, transducing coil 22 wound on a. spool 21 is aflixed with it to the inward section of reed 13 at a small gap spacing from the nearby edges of the two reed arm-mounting sections 15, so that reed 13 with its affixed coil 22 shall vibrate as a unit without interference relatively to two aflixed reed-arm mounting sections 15. The coil 22 is affixed to the reed 13 as far to the rear from its free reed end 13-1 as possible while leaving the coil spool 21 slightly spaced from the nearby edges of transverse arm ends 15.

The coil spool unit 21, 22 being aflixed to the rear part of reed 13 renders it very stiff and materially reduces the compliance of the coil-affixed reed. It is desirable to proportion the mass and compliance of the reed-coil unit to cause it to vibrate with a resonant frequency in a predetermined low audio-frequency range, for example, below 1000 c.p.s. (cycles per second), such as 900 c.p.s. and preferably a still lower frequency.

The present invention overcomes the critical difficulties encountered in securing the coil with the spool immediately adjacent to the anchored end of the thin vibratory reed which may have sharp edge or edge portions. In accordance with the invention, the two endwalls of the spool are joined to each other only by two narrow rodlike connector members engaging the opposite narrow edges of the reed which are somewhat smaller as by a few mils than the overlying width of the narrow spoolendwall connectors. After first placing the spool with the narrow spool-endwall connectors on the reed, the coil is wound on the spool-reed assembly so that the increased tension of the successive coil turns wound around the spool-reed assemblyaflixes the two spool-rod connectors against the opposite edges of the inward reed length adjoining its anchored end. Such reed-spool-coil assembly eliminates problems that would be encountered when using other type reed-spool-coil assemblies. The two narrow connector rods 21-1 of the coil spool 21 are somewhat thicker, as by 2 to 4 mils, than the facing narrow edges of the reed 13 to which they are affixed by the tension of the successive coil-wire turns wound on the previously completed reed-spool assembly 13, 21. Because the narrow connector-rods 21-1 of the spool are somewhat thicker than the thin edges of the reed, they prevent damage to the minutely thin insulation of the therearound wound coil turns by any sharp portions left on the thin edges of the reed 13. FIG. 5A is a crosssectional view along lines 5A5A of FIG. 5 showing with some dimensions exaggerated for claritys sake the relationship of the spool-junction rods 21-1 to the slightly thinner embraced edges of the reed 13.

In the manufacture of such subminiature reed transducers it is of critical importance to reduce to a minimum the number of separately produced components and the care required for their assembly into the desired operating unit.

According to the invention, a reed transducer device having an acoustic diaphragm with driving connection to the vibrating reed and the transducing coil with its spool affixed thereto is combined with a diaphragm-connected drive rod joined with its inward rod endnot directly to the reed as heretofore-but to the outward spool endwall for transmitting the vibration motion between the reed and diaphragm. The spool is usually made of plastic material. The relatively thin driving rod of the invention is likewise made of plastic motion transmitting material and its inward rod end is joined to the plastic outward spool endwall. Furthermore, such plastic diaphragm drive rod is formed or molded as part of the spool molding operation, with the drive rod being a molded part of the spool endwall from which it extends toward engagement with the diaphragm. However, under some conditions, the separately molded plastic drive rod 12 may have a somewhat wider inward rod end afiixed, as by cement, to the plastic outward spool wall.

As an example of the invention, the assembly of such transducer device is greatly simplified by providing the coil spool 21 of the reed 13 with the diaphragm-drive rod with an inward end joined to the transverse spool endwall 21 of coil spool 21 and its outer rod end aflixed in a conventional way to the intermediate portion 111 of vibratory diaphragm for transmitting vibratory motion therebetween. The drive rod 12 may be molded integrally with the molded coil spool 21. Alternatively, the inner end region of drive rod 12 is secured, as by cement, or thermoplastic bonding to facing transverse spool wall 22 (FIGS. 1, 2 and 4 to 6-).

To reduce to a minimum the effective mass of the vibratory coil-reed unit, the two opposite endwalls of coil spool 21 are joined to each other by only two opposite narrow spool connector rods 21-1 extending longitudinally along and substantially confined to the opposite narrow side edges of embraced elongated reed 13. Thus, as shown in FIGS. 2 and 5, the opposite endwalls of its spool 21 are joined to each other by only two narrow relatively rod-like side members 21-1 embracing and slightly wider than the embraced thickness of the opposite narrow reed side edges of the reed to which they are aflixed.

The specific exemplifications of the invention described above will suggest many modifications and applications thereof and the claims shall not be limited thereto.

What is claimed is:

1. In an electromagnetic reed-type acoustic transducer device,

a thin elongated vibratory reed permeable to alternating magnetic fiux having a free reed end and a transversely extending reed arm at the opposite reed end,

a magnetic core structure traversed by permanent magnetic flux having two core legs extending generally parallel to said reed and having one set of two core poles at one end and an opposite set of two core poles at the other end, said one set of core poles being spaced by a pole air gap traversed by permanent magnetic flux,

said reed arm having two outward arm sections joined to said Opposite core poles and carrying said vibratory reed for vibration with said free reed end in said pole air gap,

a spool and an insulated coil on said spool affixed with said spool to a length of said reed, adjoining said reed arm for vibration with said reed,

said spool having two longitudinally spaced transverse endwalls with said endwalls being joined to each other solely by two thin spool connectors confined substantially to the adjoining opposite narrow edges of said vibratory reed, and with the width of said connectors being greater than the corresponding width of said vibratory reed edges to protect the insulation of said coil against damage due to the presence of any sharp portions on said reed edges.

2. A reed-type acoustic transducer device as claimed in claim 1,

said coil spool with said coil and spool connectors being afiixed to an inward section of said reed adjoining said transverse reed arm.

3. A reed-type acoustic transducer device as claimed in claim 1,

said reed arm having an intermediate arm section adjoining and held for vibration with said reed,

said coil spool with said coil and spool connectors being alfixed to an inward section of said reed adjoining said intermediate arm section of said transverse reed arm.

4. In an electromagnetic reed-type acoustic transducer device,

a vibratory acoustic diaphragm,

a thin elongated vibratory reed having a driving connection to said reed and permeable to alternating magnetic flux, said reed having a free reed end and a 6 transversely extending reed arm at the opposite reed end,

a magnetic core structure traversed by permanent magnetic flux having two core legs extending generally parallel to said reed and having one set of two core poles at one end and an opposite set of two core poles at the other end, said one set of core poles being spaced by a pole air gap traversed by permanent magnetic flux,

said reed arm having two outward arm sections joined to said opposite core poles and carrying said vibratory reed for vibration with said free reed end in said pole air gap,

a spool and an insulated coil on said spool affixed with said spool to a length of said reed, adjoining said reed arm for vibration with said reed,

said spool having two spaced transverse end walls with two end wall spool connectors,

said drive connection comprising a drive rod having an outer rod end joined to said diaphragm and an inner rod end affixed to a nearby spool end wall and therethrough to the edges of said reed for securing conjoint vibrations of said reed and said diaphragm, and with the widths of said outer and inner rod ends being greater than the corresponding widths of said vibratory reed edges to protect the insulation of said coil against damage due to the presence of any sharp portions on said reed edges.

5. In an electromagnetic reed-type acoustic transducer as claimed in claim 4,

said two spaced transverse end walls with said end walls being joined to each other solely by two thin spool connectors confined substantially to the adjoining opposite narrow edges of said vibratory reed.

6. In an electromagnetic reed-type acoustic transducer as claimed in claim 4,

said reed arm having an intermediate arm section adjoining said reed,

said coil spool with said coil and spool connectors being afiixed to an inward section of said reed adjoining said transverse reed arm.

7. In an electromagnetic reed-type acoustic transducer as claimed in claim 6,

said two spaced transverse end walls with said end walls being joined to each other solely by two thin spool connectors confined substantially to the adjoining opposite narrow edges of said vibratory reed.

8. In an electromagnetic reed-type acoustic transducer device,

a vibratory acoustic diaphragm,

a thin elongated vibratory reed having a driving connection to said reed and permeable to alternating magnetic flux, said reed having a free reed end and a transversely extending reed arm at the opposite reed end,

a magnetic core structure traversed by permanent magnetic flux having two core legs extending generally parallel to said reed and having one set of two core poles at one end and an opposite set of two core poles at the other end, said one set of core poles being spaced by a pole air gap traversed by permanent magnetic flux.

said reed arm having two outward arm sections joined to said opposite core poles and carrying said vibratory reed for vibration with said free reed end in said pole air gap,

a spool and a coil on said spool afiixed with said spool to a length of said reed, adjoining said reed arm for vibration with said reed,

said spool having two spaced transverse end walls with two end wall spool connectors,

said drive connection comprising a drive rod having an outer rod end joined to said diaphragm and an inner rod end affixed to a nearby spool end wall and References Cited UNITED STATES PATENTS 3,002,058 9/1961 Knowles 179--114 8 FOREIGN PATENTS 1,119,336 12/1961 Germany.

5/1930 Great Britain. 5/ 1933 Great Britain.

KATHLEEN H. CLAFFY, Primary Examiner A. A. MCGILL, Assistant Examiner 

